©2016 Pearson Education, Inc., Hoboken, NJ. All rights reserved. Introduction Most computer programs that solve real-world problems are much larger than the programs presented in the first few chapters. Experience has shown that the best way to develop and maintain a large program is to construct it from smaller pieces, each of which is more manageable than the original program. This technique is called divide and conquer. This chapter describes some key features of the C language that facilitate the design, implementation, operation and maintenance of large programs. ©2016 Pearson Education, Inc., Hoboken, NJ. All rights reserved.

©2016 Pearson Education, Inc., Hoboken, NJ. All rights reserved.

Modularizing Programs in C Functions are used to modularize programs C programs are typically written by combining new functions you write with prepackaged functions available in the C standard library. The C standard library provides a rich collection of functions for performing common mathematical calculations, string manipulations, character manipulations, input/output, and many other useful operations. ©2016 Pearson Education, Inc., Hoboken, NJ. All rights reserved.

Modularizing Programs in C (Cont.) The functions printf, scanf and pow that we’ve used in previous chapters are standard library functions. You can write your own functions to define tasks that may be used at many points in a program. These are sometimes referred to as programmer-defined functions. The statements defining the function are written only once, and the statements are hidden from other functions. Functions are invoked by a function call, which specifies the function name and provides information (as arguments) that the called function needs to perform its designated task. ©2016 Pearson Education, Inc., Hoboken, NJ. All rights reserved.

©2016 Pearson Education, Inc., Hoboken, NJ. All rights reserved.

©2016 Pearson Education, Inc., Hoboken, NJ. All rights reserved.

©2016 Pearson Education, Inc., Hoboken, NJ. All rights reserved.

©2016 Pearson Education, Inc., Hoboken, NJ. All rights reserved.

©2016 Pearson Education, Inc., Hoboken, NJ. All rights reserved.

©2016 Pearson Education, Inc., Hoboken, NJ. All rights reserved.

©2016 Pearson Education, Inc., Hoboken, NJ. All rights reserved.

©2016 Pearson Education, Inc., Hoboken, NJ. All rights reserved.

©2016 Pearson Education, Inc., Hoboken, NJ. All rights reserved. 5.9  Passing Arguments By Value and By Reference. WE WILL COVER THIS TOPIC IN POINTERS In many programming languages, there are two ways to pass arguments—pass-by-value and pass-by-reference. When arguments are passed by value, a copy of the argument’s value is made and passed to the called function. Changes to the copy do not affect an original variable’s value in the caller. When an argument is passed by reference, the caller allows the called function to modify the original variable’s value. Pass-by-value should be used whenever the called function does not need to modify the value of the caller’s original variable. ©2016 Pearson Education, Inc., Hoboken, NJ. All rights reserved.

©2016 Pearson Education, Inc., Hoboken, NJ. All rights reserved. 5.9  Passing Arguments By Value and By Reference (Cont.) WE WILL COVER THIS TOPIC IN POINTERS This prevents the accidental side effects (variable modifications) that so greatly hinder the development of correct and reliable software systems. Pass-by-reference should be used only with trusted called functions that need to modify the original variable. In C, all arguments are passed by value. In Chapter 6, we’ll see that array arguments are automatically passed by reference for performance reasons. ©2016 Pearson Education, Inc., Hoboken, NJ. All rights reserved.

©2016 Pearson Education, Inc., Hoboken, NJ. All rights reserved.

©2016 Pearson Education, Inc., Hoboken, NJ. All rights reserved.

©2016 Pearson Education, Inc., Hoboken, NJ. All rights reserved.

©2016 Pearson Education, Inc., Hoboken, NJ. All rights reserved.

©2016 Pearson Education, Inc., Hoboken, NJ. All rights reserved.

©2016 Pearson Education, Inc., Hoboken, NJ. All rights reserved.  Scope Rules ©2016 Pearson Education, Inc., Hoboken, NJ. All rights reserved.

©2016 Pearson Education, Inc., Hoboken, NJ. All rights reserved.   Scope Rules (Cont.) static still have block scope, even though they exist from before program startup. ©2016 Pearson Education, Inc., Hoboken, NJ. All rights reserved.

©2016 Pearson Education, Inc., Hoboken, NJ. All rights reserved.

©2016 Pearson Education, Inc., Hoboken, NJ. All rights reserved.

©2016 Pearson Education, Inc., Hoboken, NJ. All rights reserved.

©2016 Pearson Education, Inc., Hoboken, NJ. All rights reserved.

©2016 Pearson Education, Inc., Hoboken, NJ. All rights reserved. Preprocessor ©2016 Pearson Education, Inc., Hoboken, NJ. All rights reserved.

©2016 Pearson Education, Inc., Hoboken, NJ. All rights reserved. #include <stdio.h> #if 0 #define DUMMY 20 #else #define DUMMY 10 #endif int main(){ printf("%d\n",DUMMY); return 0; } #include <stdio.h> #define TEMP 10 #if defined(TEMP) #define DUMMY 20 #else #define DUMMY 10 #endif int main(){ printf("%d\n",DUMMY); return 0; } ©2016 Pearson Education, Inc., Hoboken, NJ. All rights reserved.

©2016 Pearson Education, Inc., Hoboken, NJ. All rights reserved. Header Files ©2016 Pearson Education, Inc., Hoboken, NJ. All rights reserved.

©2016 Pearson Education, Inc., Hoboken, NJ. All rights reserved.

©2016 Pearson Education, Inc., Hoboken, NJ. All rights reserved.

©2016 Pearson Education, Inc., Hoboken, NJ. All rights reserved. So far Putting all what we learnt together in the next lab and on the last lecture of this week (Thursday). ©2016 Pearson Education, Inc., Hoboken, NJ. All rights reserved.

©2016 Pearson Education, Inc., Hoboken, NJ. All rights reserved. Recursion ©2016 Pearson Education, Inc., Hoboken, NJ. All rights reserved.

Simple Recursion example #include <stdio.h> void rec(int n); int main() { int n =6; rec(n); return 0; } void rec(int n) { printf("%d ",n); if (n==0) return; else return(rec(n-1)); ©2016 Pearson Education, Inc., Hoboken, NJ. All rights reserved.